Dual Stage Actuated Suspension Having Shear-Mode PZT Actuators for Rotating Gimbal Tongue

ABSTRACT

A dual stage actuated (DSA) suspension uses two shear-mode PZT microactuators to finely position the head slider. The bottom surfaces of the PZTs are affixed to the flexure, and the PZT top surfaces move forward and backward, respectively, in push-pull fashion when the PZTs are activated. Flexible connector arms attach the tops surfaces of the PZTs to the gimbal tongue such that activating the PZTs causes the gimbal tongue to rotate, with the connector arms acting as levers to magnify the motion such that a relatively small shear movement of the PZTs results in a significantly larger lateral movement of the head slider across the data disk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patentapplication No. 62/216,941 filed Sep. 10, 2015, the disclosure of whichis incorporated by reference as if set forth fully herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to the field of suspensions for disk drives. Moreparticularly, this invention relates to the field of a dual stageactuated suspension having shear-mode PZT actuators that rotate thegimbal tongue.

2. Description of Related Art

In a typical disk drive assembly, the suspension is the part that holdsthe read/write head over the correct position on a spinning data disksuch as a magnetic data medium or optical data medium containing anumber of concentric data tracks. The suspension typically includes abeam portion or load beam, and a flexure that includes a gimbaledportion, with the load beam typically mounted to a baseplate at theproximal end of the suspension, and the flexure mounted at the distalend of the load beam. The read/write head, or head slider, is affixed tothe gimbaled portion of the flexure so that it can pitch and rollfreely. The suspension is typically mounted at the end of an actuatorarm, with the actuator arm moved by a voice coil motor (VCM).

Dual stage actuated (DSA) suspensions are well known. In a DSAsuspension, the suspension is not only activated by the voice coil motorwhich moves the entire suspension, but an additional actuator is placedon the suspension itself for effecting fine movements of the head sliderin order to keep it properly aligned over the correct data track on thespinning disk. The secondary actuator(s) provide finer control andhigher bandwidth of the servo control loop than does the voice coilmotor alone, which is only capable of effecting relatively coarse, slowmovements of the suspension and hence the head slider. The secondaryactuator(s) are sometimes referred to as milliactuators if they aremounted near the proximal end of the suspension, and microactuators ifthey are mounted near the distal end of the suspension. As used herein,the term “microactuator” will be used as an umbrella term that refers toany small actuator motor that is located on the suspension itself. Apiezoelectric element, sometimes referred to simply as a PZT, is oftenused as the microactuator motor, although other types of microactuatormotors are possible.

In order to achieve the best performance in a suspension, it isimportant to maximize the stroke length in the microactuation mechanism.The term “stroke length” is a shorthand expression for the distance thatthe read/write head moves radially across a data disk per unit ofvoltage input to the microactuator motor.

Linear-mode PZTs are commonly used as microactuators on DSA suspension.U.S. Pat. No. 8,879,210 issued to Hahn et al. is an example of a DSAsuspension that uses linear-mode PZTs to position the read/write head.The two PZTs act in push-pull fashion to rotate the head slider and thusto precisely position its read/write transducers.

D₃₁ is the transverse piezoelectric coefficient of a linear-modepiezoelectric device; it represents the amount of linear expansion a PZTdevice undergoes in the transverse direction (i.e., normal to theelectric field gradient) when an activation voltage is placed across thedevice's electrodes. D₃₃ is the longitudinal piezoelectric coefficient;it represents the amount of linear expansion of a PZT in thelongitudinal direction (i.e., in the direction of the electric fieldgradient) when an activation voltage is placed across the device'selectrodes.

SUMMARY OF THE INVENTION

In addition to linear-mode PZTs, shear-mode PZTs exist. In a shear-modePZT, in response to an activation voltage the PZT deforms in shear. Forexample, the top surface moves horizontally relative to the bottomsurface. D₁₅ is the shear piezoelectric coefficient of a shear-mode PZT.The present invention employs a shear-mode PZT operating in the d₁₅mode, or shear mode, in order to maximize the stroke length.

According to an exemplary embodiment, first and second shear-mode PZTsoperating in the d₁₅ mode are mounted on a flexure. The PZTs may bemounted on separate flexible outrigger arms than can flex in thevertical dimension at least somewhat independently. Respective first andsecond flexible connector arms extend from the PZTs to the gimbaltongue. When the PZTs are activated, the two PZTs act in oppositedirections in push-pull fashion, thereby pushing on and pullingrespectively opposite sides of the gimbal tongue through the respectiveconnector arms, to rotate the gimbal tongue together with the headslider that is mounted on the gimbal tongue. Rotating the gimbal tonguepositions the read/write data transducers that are embedded in the headslider, usually close to the distal end of the slider, over the desireddata track on the data disk. The mechanical coupling from the PZTs tothe head slider acts as a lever to magnify the shear movement of thePZTs into significantly greater spatial displacement at the read/writetransducers.

The gimbal tongue may be supported by only the flexible connectors, withthe freedom of movement provided by the flexible connectors combiningwith the freedom of movement provided by the independently flexingflexible outrigger arms to provide the desired gimbaling action at thehead slider in the pitch and roll directions.

Exemplary embodiments of the invention will be further described belowwith reference to the drawings, in which like numbers refer to likeparts. The drawing figures might not be to scale, and certain componentsmay be shown in generalized or schematic form and identified bycommercial designations in the interest of clarity and conciseness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top oblique view of a suspension according to an exemplaryembodiment of the invention.

FIG. 2 is a top plan view of the trace gimbal assembly of the suspensionof FIG. 1.

FIG. 3 is a bottom plan view of the trace gimbal assembly of FIG. 2.

FIG. 4 is a top oblique view of the flexure gimbal of FIG. 2.

FIG. 5 is a closeup of the flexure gimbal of FIG. 4.

FIG. 6 is a bottom oblique view of the flexure gimbal of FIG. 4

FIG. 7A is a cross sectional view of the flexure of FIG. 5, taken alongsection line 7A-7A, when the PZTs are activated.

FIG. 7B is a cross sectional view of the flexure of FIG. 5, taken alongsection line 7B-7B, when the PZTs are activated.

FIG. 8 is a side sectional view of the flexure of FIG. 5 taken alonesection line 8-8.

FIG. 9 is a top plan view of the flexure of FIG. 4 when the PZTs areactivated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the “bottom” side of a suspension is the side on whichthe read/write head is mounted, i.e., the side which faces the datadisk, and the “top” side is the side opposite the bottom side. The“proximal” end of a suspension or load beam is the end that issupported, i.e., the end nearest to the base plate which is swaged orotherwise mounted to an actuator arm. The “distal” end of a suspensionor load beam is the end that is opposite the proximal end, i.e., the“distal” end is the cantilevered end.

FIG. 1 is a top oblique view of a suspension 2 according to an exemplaryembodiment of the invention. Suspension 2 includes: a base plate 4; anda load beam 6, or beam portion, or simply beam extending from baseplate4 and attached to baseplate 4 via hinge springs at a proximal end ofload beam 6. A trace gimbal assembly (TGA) 10 which carries head slider42 is attached to load beam 6 at the distal end of load beam 6.

FIG. 2 is a top plan view of TGA 10 of the suspension 2 of FIG. 1, andFIG. 3 is a bottom plan view thereof. TGA 10 includes flexure 11 andflexible circuit 9. Flexible circuit 9 includes layers of a dielectricinsulator which is typically polyimide, and electrical signal tracesformed of a conductor which is typically copper or copper alloy. Bothload beam 6 and the flexure 11 are typically made of stainless steel,and are typically welded together using laser spot welding. Flexure 11includes two elongate flexible outrigger arms 12 on the left and rightlateral sides of the flexure, and outer gimbal ring 18. The proximal endof flexure 11 is connected to load beam 6 and is therefore relativelyfixed. Because outrigger arms 12 are thin and flexible, their distalends can move vertically relative to one another relatively freely asthe outrigger arms 12 flex up and down and without any direct rigidcoupling between those distal ends. Head slider 42 is bonded and rigidlyaffixed to gimbal tongue 40 such as by epoxy adhesive. Flexible circuit9 carries read/write signals and data tracking servo control loopsignals to and from head slider 42.

FIG. 4 is a top oblique view of the distal portion of flexure 11 of FIG.2. Flexible circuit 9 is not shown for clarity of illustration.Outrigger arms 12 include generally laterally extending portions 13.Gimbal tongue 40 defines a gimbaled portion 14 of the TGA 10 to whichhead slider 42 is mounted, and hence gimbal tongue 40 also defines agimbaled portion of suspension 2.

FIG. 5 is a closeup of the flexure gimbal of FIG. 4, showing the PZTsand their mechanical coupling to gimbal tongue 40 in detail. Flexibleoutrigger arms 12 include generally laterally extending portions 13,portions of which define bases 20, 30 on which one, and preferably two,piezoelectric devices 22, 32 are mounted. The piezoelectric devices 22,32 define microactuators, which will be referred to simply as PZTs. PZTs22, 32 operate in the d₁₅ mode; such PZTs are referred to as shear-modePZTs.

PZTs 22, 32 are attached at the distal ends of respective flexibleoutrigger arms 12. In the preferred embodiment there is no directmechanical connection extending between the two PZTs or tying themclosely together. The PZTs 22, 32 thus enjoy a certain amount of freedomof movement such that one PZT 22 can move vertically relative to theother PZT 32.

PZTs 22, 32 can be bonded directly to flexible outrigger arms 12.Because flexure 11 is typically made of stainless steel which iselectrically conductive and is grounded through load beam 6, if PZTs 22,32 are bonded to flexible outrigger arms 12 using conductive adhesivesuch as epoxy containing silver particles, then assuming that the bottomsurfaces of the PZTs are electrodes, the bottom electrodes are thusgrounded; the actuating drive voltage for the PZTs would be supplied tothe drive electrode which would normally be located on the top surfaceof the PZTs. If the PZTs are electrically isolated from flexibleoutrigger arms 12 such as via the insulating layer of the TGA 10, theneither the top or bottom surface can be the drive electrode, with theother surface being the ground electrode. Although normally the top andbottom surfaces of the PZTs constitute the two electrodes for thedevice, other possibilities exist including PZTs having wrap-aroundelectrodes such that both electrodes are accessible from a single faceof the PZT.

The actual electrical connections to the PZTs 22 and 32 are omitted forclarity of illustration. Examples of electrical connections to PZTs insuspensions can be seen in, e.g., U.S. Pat. No. 8,254,065 to Inoue etal.; U.S. Pat. No. 9,251,817 to Hahn et al.; U.S. Pat. No. 8,810,972 toDunn; and U.S. Pat. No. 8,189,301 to Schreiber. The actual connectionsof the PZT actuating voltage and ground to the PZTs is a matter ofdesign choice; a number of possibilities would be apparent to thedesigner of ordinary skill in the art of suspension design.

PZTs 22, 32 are coupled to gimbal tongue 40 via flexible connector 50.Connector 50 includes left connector arm 24 which includes generallylongitudinally extending portion 25 and generally laterally extendingportion 26, and right connector arm 34 which includes generallylongitudinally extending portion 35 and generally laterally extendingportion 36. Connector arms 24, 34 may be bonded to PZTs 22, 32 such asby epoxy adhesive. Preferably connector 50 is unitarily formed of asingle piece of spring material such as stainless steel. The generallylongitudinally extending portions 25, 35 are angled slightly inwardly,preferably at an angle of 0-30°, so that as they extending distally fromthe PZTs they also extend slightly inwardly toward a centrallongitudinal axis of the flexure and of the suspension. In theembodiment shown, connector 50 attaches to gimbal tongue 40 at a singlelocation that corresponds to spacer or standoff 44, and gimbal tongue 40is supported only by connector 50, such that connector 50 including itsflexible connector arms 24, 34 provide the sole mechanical support forgimbal tongue 40. The freedom of movement provided by flexible outriggerarms 12 combined with the freedom of movement provided by flexibleconnector 50 provides a gimbaling action that allows head slider 42 topitch and roll freely to accommodate vibrations, inertial events such asbumping, and irregularities in the disk platter surface as the diskplatter moves underneath the head slider. Preferably the generallylongitudinally extending portions 25, 35 of connector 50 are narrower inthe lateral direction than PZTs 22, 32. More preferably, portions 25, 35of connector 50 are less than one third as wide as the lateral widths ofeach of the PZTs 22, 32.

In the embodiment, generally laterally extending portions 26, 36 ofconnector 50 are connected to gimbal tongue 40 via standoff 44 whichseparates connector 50 from gimbal tongue 40 by approximately the samedistance as thicknesses of PZTs 22, 32, such as a distance that is50%-150% of the thicknesses of the PZTs. Standoff 44 could be conductiveepoxy to electrically connect to the tongue. Alternatively, connector 50and gimbal tongue 40 could be welded together. If connector 50 comprisesan electrically conductive material such as stainless steel and isbonded to the PZTs using conductive adhesive such as conductive epoxy,then a single common PZT driving voltage could be supplied to one of thePZTs' top electrodes, and connector 50 will carry that driving voltageto the other PZT's top electrode. Thus, using connector 50, only asingle driving voltage connection is necessary in order to drive bothPZTs.

FIG. 6 is a bottom oblique view of the flexure gimbal of FIG. 4.

FIG. 8 is a side sectional view of the flexure of FIG. 5 taken alonesection line 8-8.

FIG. 7A is a cross sectional view of the flexure of FIG. 5, taken alongsection line 7A-7A, when the PZTs are activated, and FIG. 7B is a crosssectional view of the flexure of FIG. 5 taken along section line 7B-7B,when the PZTs are activated. When PZTs 22, 32 are activated by applyinga voltage across their electrodes 27/29 and 37/39, PZT 22 moves inshear, i.e. in its d₁₅ mode, with its top surface 29 moving in a moredistal direction while PZT 32 moves in shear with its top surface 39moving in a more proximal direction, as shown in FIGS. 7A and 7B, orvice versa. Connector 50 defines a mechanical coupling that couples thepush-pull movement of PZTs 22, 32 into rotational movement of gimbaltongue 40 and hence of head slider 42. Connector 50, and in particularthe generally longitudinally extending portions 25, 35, act as leverarms to multiply the relatively small longitudinal movements of topfaces 29, 39 of PZTs 22, 32 to a much larger lateral movement at gimbaltongue 40 and hence at the center of head slider 42 and also at theparticular loci where the read and write magnetic data transducers arelocated within head slider 42. Additionally, because the d₁₅ (shear)coefficient of PZT devices is generally higher than the d₃₁ (linear)coefficient, using shear-mode PZTs, particularly coupled with amechanical coupling such as the one disclosed herein to amplify theshear movement of the PZTs, produces a large stroke length, which is thehighly desired result.

The PZTs are poled and mounted such that a single common activationvoltage applied to the top electrodes at top surfaces 29 and 39 causesPZT 22 to shear in the forward direction indicated by the arrow in FIG.7A, and PZT 32 to simultaneously shear in the backward directionindicated by the arrow in FIG. 7B. That is, the top surface 29 of PZT 22moves towards gimbal tongue 40 thus pushing a first side of gimbaltongue 40, and the top surface 39 of PZT 32 moves away from gimbaltongue 40 thus pulling a second side of the tongue that is laterallyopposite the first side. When that happens, the mechanical couplingincluding connector 50 causes the head slider to rotate, which moves thedata read and data write transducers embedded within the head slideracross the data disk laterally, i.e., in a direction that isperpendicular to the data tracks on the disk. The rotational motion ofthe gimbal tongue therefore causes the head slider to be positionedproperly over the data track, or moved to a different data trackaltogether.

In the embodiment, a proximal tail portion 41 of gimbal tongue 40extends between the two PZTs 22, 32, such as at least as far as themidpoint of PZTs 22, 32. Tail portion 41 can provide moment-balancingfor gimbal tongue 40. Furthermore, tail portion 41 may be formed such asby bending to interact with other features of the flexure to act as avertical travel limiter for head slider 42.

FIG. 9 is a top plan view of the flexure of FIG. 4 when the PZTs areactivated such as shown in FIGS. 7A and 7B. The top surface of PZT 22has moved in shear toward the distal end of the suspension, and thebottom surface of PZT 32 has moved in shear toward the proximal end ofthe suspension. Acting through connector 50, the shear movement of thePZTs acts in push/pull fashion to rotate gimbal tongue 40 and hence headslider 42. The magnetic read/write transducers (not shown) that areembedded in head slider 42 therefore move with a radial component acrossthe concentric data tracks on the data disk (not shown) within the diskdrive assembly.

It will be understood that the terms “generally,” “approximately,”“about,” and “substantially,” as used within the specification and theclaims herein allow for a certain amount of variation from any exactdimensions, measurements, and arrangements, and that those terms shouldbe understood within the context of the description and operation of theinvention as disclosed herein.

It will further be understood that terms such as “top,” “bottom,”“above,” and “below” as used within the specification and the claimsherein are terms of convenience that denote the spatial relationships ofparts relative to each other rather than to any specific spatial orgravitational orientation. Thus, the terms are intended to encompass anassembly of component parts regardless of whether the assembly isoriented in the particular orientation shown in the drawings anddescribed in the specification, upside down from that orientation, orany other rotational variation.

It will also be appreciated that the term “present invention” as usedherein should not be construed to mean that only a single inventionhaving a single essential element or group of elements is presented.Similarly, it will also be appreciated that the term “present invention”encompasses a number of separate innovations which can each beconsidered separate inventions. Although the present invention has thusbeen described in detail with regard to the preferred embodiments anddrawings thereof, it should be apparent to those skilled in the art thatvarious adaptations and modifications of the present invention may beaccomplished without departing from the spirit and the scope of theinvention. For example, a suspension could employ only a single PZT,and/or could employ mechanical coupling mechanisms other than theexemplary coupling mechanism shown in the drawings. Accordingly, it isto be understood that the detailed description and the accompanyingdrawings as set forth hereinabove are not intended to limit the breadthof the present invention, which should be inferred only from thefollowing claims and their appropriately construed legal equivalents.

1. A dual stage actuated suspension for a disk drive, comprising: a beamportion; a flexure mounted to the beam portion, the flexure including:first and second flexible outrigger arms extending on respective lateralsides of the flexure from a relatively fixed portion of the flexure; anda gimbal tongue; a head slider mounted to the gimbal tongue for writingdata to, and reading data from, a moving data medium containing aplurality of data tracks thereon; a first shear-mode piezoelectricdevice mounted at a distal end of the first flexible outrigger arm, thefirst shear-mode piezoelectric device having a top surface, a bottomsurface, and two electrodes, the top surface moving in a linear sheardirection relative to the bottom surface when an actuation voltage isapplied across the electrodes; and a mechanical coupling that, inresponse to the piezoelectric device being activated, couples the shearmovement of the piezoelectric device to rotational movement of the headslider.
 2. The suspension of claim 1 further comprising: a secondshear-mode piezoelectric device mounted at a distal end of the secondflexible outrigger arm, the second shear-mode piezoelectric devicehaving a top surface and a bottom surface; wherein when the first andsecond piezoelectric devices are actuated, the top surface of the firstpiezoelectric devices moves in a first direction and the top surface ofthe second piezoelectric devices moves in a second direction generallyopposite the first direction such that the two piezoelectric devicesoperate in push-pull fashion to produce push-pull movement, themechanical coupling translating the push-pull movement of the shear-modepiezoelectric devices to rotate the head slider.
 3. The suspension ofclaim 1 wherein the mechanical coupling multiplies movement of thepiezoelectric device so as to cause a small movement of thepiezoelectric device to produce a relatively larger movement at a centerof the head slider.
 4. The suspension of claim 1 wherein the gimbaltongue is supported only by said mechanical coupling.
 5. (canceled) 6.(canceled)
 7. The suspension of claim 14 wherein the flexible connectorhas a width that is less than one third a lateral width of thepiezoelectric devices.
 8. (canceled)
 9. A dual stage actuated suspensionfor a disk drive, comprising: a beam portion; a flexure mounted to thebeam, the flexure including a gimbal tongue and a head slider mounted tothe gimbal tongue for writing data to, and reading data from, a movingdata medium, the gimbal tongue being gimbaled on the flexure to allowthe head slider to pitch and roll as the moving data medium movesunderneath the head slider; first and second shear-mode piezoelectricdevices flexibly mounted to the flexure such that said first and secondshear-mode piezoelectric devices have freedom of movement to movevertically without being rigidly coupled to each other in the verticaldimension; a mechanical coupling arranged so that activation of thefirst piezoelectric device causes a pushing force to be exerted on afirst side of the gimbal tongue at the same time that activation of thesecond piezoelectric devices causers a pulling force to be exerted on asecond side of the gimbal tongue opposite the first side, thesimultaneous pushing and pulling forces on the gimbal tongue causing thegimbal tongue to rotate.
 10. The suspension of claim 9 wherein: thefirst and second piezoelectric devices are mounted on respective firstand second flexible outrigger arms extending from a relatively fixedportion of the suspension; and freedom of movement provided by theflexible outrigger arms combined with freedom of movement provided bythe elongate flexible arms provide gimbaling action that allows the headslider to pitch and roll freely.
 11. The suspension of claim 9 whereinthe gimbal tongue is supported only by flexible connectors extendingfrom the first and second piezoelectric devices to the gimbal tongue.12. The suspension of claim 9 wherein the first and second piezoelectricdevices are separately supported such that the first piezoelectricdevice can move vertically relative to the second piezoelectric device.13. A dual stage actuated suspension for a disk drive, comprising: abeam; a flexure mounted to the beam, the flexure including a gimbaltongue and a head slider mounted thereto for writing data to, andreading data from, a moving data medium, the gimbal tongue beinggimbaled on the flexure to allow the head slider to pitch and roll asthe moving data medium moves underneath the head slider; a shear-modepiezoelectric device mounted to the flexure; and a flexible connectorextending from the shear-mode piezoelectric device to the gimbal tongue;wherein when the piezoelectric device is actuated: the shear-modepiezoelectric device moves the flexible connector in a firstlongitudinal direction; and the movement of the flexible connectorcauses the head slider to rotate.
 14. The suspension of claim 13wherein: the shear-mode piezoelectric device and the flexible connectorrespectively define a first shear-mode piezoelectric device and a firstflexible connector; and the suspension further comprises: a secondshear-mode piezoelectric device mounted to the flexure; and a secondflexible connector extending from the second shear-mode piezoelectricdevice to the gimbal tongue; wherein when the second piezoelectricdevice is activated: the second shear-mode piezoelectric device movesthe second flexible connector in a second longitudinal directionopposite the first longitudinal direction.
 15. The suspension of claim14 wherein the two flexible connectors are unitarily formed of a singlepiece of material, and connect to the gimbal tongue at a singlelocation.
 16. The suspension of claim 15 wherein the gimbal tongue issupported only by the flexible connector.
 17. The suspension of claim 14wherein the two flexible connectors are unitarily formed of a singlepiece of stainless steel and carry a common driving voltage to the twopiezoelectric devices.
 18. The suspension of claim 14 further comprisinga standoff that separates the flexible connector from a surface of thegimbal tongue by a distance that approximately equals a thickness offirst piezoelectric device.
 19. The suspension of claim 14 wherein theflexible connectors have a width that is less than one third a lateralwidth of each of the piezoelectric devices.
 20. The suspension of claim14 wherein as the flexible connectors extend distally from thepiezoelectric devices, they also extend laterally inwardly toward acentral longitudinal axis of the flexure.